The present invention relates generally to methods and systems for generating a buried insulating layer in a semiconductor substrate. More particularly, the invention provides methods and systems for forming a buried oxide layer in a semiconductor substrate, such as, silicon.
One method known in the art as Separation by Implantation of Oxygen (SIMOX) forms a thin buried oxide (BOX) layer in a semiconductor substrate, such as silicon, by bombarding the substrate with energetic oxygen ions at a high dose. Typically, the substrate is heated to a temperature of about 400° C. to 600° C. during this implantation so that damage to crystal structure of the substrate is offset, in part, by “self-annealing.”Following implantation, residual damage in the substrate is removed and buried oxide layer is formed by a further annealing step at an elevated temperature of about 800° C. or higher. The buried oxide layer can function as an insulating layer that separates an upper semiconductor layer from the bulk semiconductor. This allows formation of devices on the upper silicon layer with better performance characteristics, such as, enhanced speed and reduced power consumption. Devices formed on a silicon substrate having a buried oxide layer, known as silicon-on-insulator (SOI) devices, are routinely utilized in a number of technological applications.
A variety of modifications to the basic SIMOX process described above have been proposed in the art to enhance the efficiency of the formation of the buried oxide layer and its characteristics. In one such method, an initial implantation step is followed by a second implantation step, generally known as a touch-up or damage engineering implant, at a significantly lower oxygen dose. Wafer heating is often stopped during this touch-up process and energy of the ions can also be modified. The effect of the touch-up implant is to increase the damage to the layer in which the implanted oxygen ions are deposited and/or a layer in proximity thereof. The touch-up implant is then followed, for example, by a conventional annealing step to generate a single crystal surface layer of silicon and a continuous buried layer of silicon dioxide. The touch-up implant provides a number of advantages. For example, if the annealing is carried out in an oxygen-containing atmosphere, the touch-up implant can facilitate the reaction of oxygen atoms diffused to the damaged layer and increase layer efficiency for trapping diffused oxygen atoms during the annealing step, thereby enhancing the continuity and the growth of the buried oxide layer.
There is, however, still a need for providing improved SIMOX processes and systems that would allow a more efficient formation of the buried oxide layer, and further would enhance the characteristics of the buried oxide layer, such as, its thickness and its uniformity.